A phenolic resin foam used as a thermal-insulating material can provide required thermal insulation performance in a thinner thickness as the phenolic resin foam has lower thermal conductivity, thereby reducing the amount of the thermal-insulating material used and reducing space required for construction. In a residential house, for example, a wider effective living space can be secured to the construction area of the residential house.
In addition, once the residential house is constructed, the residential house is used for a long period and thus high thermal insulation performance should be maintained for a long period.
In recent years, long-term quality housing has been required more and more because of energy saving and resource saving and thus the high thermal insulation performance and retention of initial low thermal conductivity for a longer period are required more than ever before.
Patent Literature 1 discloses a phenolic resin foam characterized in that the foam has 5% or less of the area ratio of voids relative to the cross-sectional area of the foam and in which holes do not substantially exist in a cell wall. The phenolic resin foam, however, has insufficient initial thermal conductivity and a change rate in aged thermal conductivity.
Patent Literature 2 discloses a foamable phenolic resole resin composition characterized in containing a foaming agent including cyclopentane as a main component and a partial hydrolysis-condensation product of an organic silicon compound having a hydrolyzable group. The foamed phenolic resin foam, however, has high initial thermal conductivity and large increase in aged thermal conductivity.
Patent Literature 3 discloses a phenolic resin foam characterized in containing a filler selected from a metal hydroxide, a metal oxide, a metal carbonate, and a metal powder and having a pH of 5 or more. The phenolic resin foam, however, has high initial thermal conductivity and large increase in aged thermal conductivity.
Patent Document 4 discloses a phenolic resin foam characterized in that the foam has a uniform fine cell structure in which the standard deviation of a cell diameter distribution is 7% or less of an average cell diameter and the area ratio of voids existing in the cross-sectional area of the foam is 0.5% or less, and in which holes do not exist in a cell wall. The phenolic resin foam, however, has insufficient initial thermal conductivity and the change rate in aged thermal conductivity.